This invention relates to electroless plating operations.
Electroless copper plating is a significant step in the fabrication of printed circuit boards. Currently, 15 to 25 percent of the operating electroless chemistry volume per plating cycle becomes waste due to by-product buildup. Consequently, economical methods for treating this waste need to be devised to avoid conflict with present and future environmental regulations.
For example, the effluent from a typical electroless copper bath comprises high levels of formaldehyde (approximately 2.4 gms/liter), ethylenediamine tetraacetic acid (EDTA) (approximately 42 gms/liter), and formate (approximately 15 gms/liter). According to 1995 discharge guidelines, the amount of formaldehyde should be reduced to 14 ppm, and the amount of EDTA should be reduced to 90 ppm. There is currently no limit on the amount of formate, but high levels of formate are known to lower the ratio of biological oxygen demand (BOD) to chemical oxygen demand (COD) which may upset the delicate biological environment in public treatment systems. An efficient method of organic destruction will need to impact all three constituent levels.
A further problem in electroless copper plating is the fact that the rinse water in the process also becomes contaminated with the above constituents and needs to be treated.
It is known that hydrogen peroxide can destroy the organic content of the waste stream from an electroless copper plating bath. However, the hydrogen peroxide alone cannot reduce the organics to acceptable levels in a timely manner. Thus, it has been proposed to simultaneously add hydrogen peroxide and subject the waste to irradiation by UV light, followed by subjecting the resulting composition to an ozone gas with a second irradiation by UV light. (See, e.g., U.S. Pat. No. 4,512,900 issued to Macur et al.) While such a technique may be effective, it is also expensive.
It has also been proposed to treat waste streams in general with a combination of hydrogen peroxide and irradiation with UV light. (See U.S. Pat. No. 4,012,321 issued to Koubek.) However, no teaching specific to reducing organic waste from electroless plating operations is provided.